FIG. 1 shows a transmitter according to the prior art. A data source generates source data symbols which is [sic] output by the data symbol source via a line to what is termed a Tomlinson precoding filter. The Tomlinson precoding filter is generally a non-recursive digital filter whose filter coefficient [sic] are set as a function of the properties of the data transmission line. The Tomlinson precoding filter receives the source data symbols d from the data source with a symbol clock frequency fT. The source data symbols d are generally multi-level symbols and have a number of levels N. The Tomlinson precoding filter processes the received source data symbols d with the symbol clock frequency fT and outputs output values p to a downstream digital transmission filter. As a result of the Tomlinson precoding filter, the output values of the output signal p lie only within a prescribed value region, and so the peak value is also limited to this overload point of the value range. This has the consequence that the requirements made of the circuitry at the downstream line driver within the transmitter do not become excessively high.
The line driver, which is used in the case of an SDL (symetrical [sic] digital subscriber line), for example, is of complex design in terms of circuitry, since because of the data transmission in upstream and downstream directions in the same frequency band is performed [sic] and there is a consequent need for echo compensation in the receiver. Consequently, the line driver must exhibit a linearity which in part is more than 80 dB. The line amplifier carries out signal amplification of the transmission signal, the transmit power generally being prescribed by the standardization.
The outlay on circuitry for the line driver increases for a prescribed transmit power with an increasing peak valve of the output voltage of the transmission signal. In this case, the crest factor defines the ratio of the peak voltage to the r.m.s. voltage, and is mostly specified in decibels. The crest factor can assume values of up to 10 dB and more, depending on pulse shaping. The crest factor increases with increasing output voltage peak value of the transmission signal, and therefore rises with the magnitude of the dynamic range.
FIG. 2 shows a Tomlinson precoding filter according to the prior art, which is installed in the conventional transmitter as it is illustrated in FIG. 1. This conventional Tomlinson precoding filter includes a modulo adder, which adds the source data symbols d, which are received from the data symbol source with the symbol clock frequency fT at a signal input E of the precoding filter, with fedback filtered transmission data symbols r, which are filtered by a feedback filter, to transmission data symbols p which are output via a signal output A of the Tomlinson precoding filter to the downstream transmission filter. Given a number of levels N for the source data symbols N, the transmission data symbols output by the precoding filter assume the following values:
  P  =            1      N        ⁢          {                        -                      (                          N              -              1                        )                          ,                                            (                              N                -                3                            )                        ⁢                                                  ⁢            …                    -          1                ,                  1          ⁢                                          ⁢          …          ⁢                                          ⁢                      (                          N              -              3                        )                          ,                              (                          N              -              1                                }                    In the case of a four-level transmission, for example, the following values are yielded: 0.75, −0.25, 0.25, 0.75.
The modulo addition of the modulo adder is performed as follows:
                              p          =                      d            +            r                                                        p          =                      d            +            r            -                          n              ⁢              .2                                                                    p          =                      d            +            r            +                          n              ⁢              .2                                            ⁢                              if          ⁢                                          |                      d            +            r                    |                      ≤            1                                                                    if            ⁢                                                  |            d                    =                      r            |                          >              1                                                                                if            ⁢                                                  |                          d              +              r                        |                          <                              -                1                                              ,                    n being integral and selected such that the output value p lies only within a dynamic range of −1 to +1.
FIG. 3 shows the amplitude distribution downstream of the Tomlinson precoding filter and of the downstream digital transmission filter in the case of the conventional transmitter as it is illustrated in FIG. 1. The dynamic range of the Tomlinson precoding filter is between −1 and +1, while the dynamic range of the digital transmission filter is between −1.7 and +1.7. The amplitude distribution downstream of the transmission filter, and thus the peak values of the output signal, are relatively high. Owing to the spectral shaping because of the downstream digital transmission filter, the dynamic range and thus the crest factor of the output signal is [sic] relatively high. The circuitry arrangement according to the prior art as it is illustrated in FIG. 2 therefore has the disadvantage that, owing to the high crest factor of the output signal output by the digital transmission filter, the requirements made on the circuitry of the line driver are likewise relatively high.